Auxiliary power units (“APU”) are used in aircraft to provide electrical power and compressed air to various parts therein. When an aircraft is on the ground, its main source of electrical power comes from the APU. In particular, the APU can power the electrical systems, environmental control systems, air drive hydraulic pumps, and the starters for the engines. When an aircraft is in flight, the APU may provide pneumatic and/or electric power to the aircraft.
Typically, an APU is located in the aft section of the aircraft, at or near the tailcone section. The APU is coupled to exhaust ducting that exits through an opening in the aircraft fuselage to allow sufficient air flow therethrough. Additionally, the exhaust ducting may be used to evacuate gases that may be exhausted from the APU, provide cooling air to the APU via an eductor system, and allow exit of APU exhaust noises from the aircraft.
As acceptable noise threshold levels have decreased, more APU exhaust ducting configurations have included noise attenuation devices, such as mufflers. Although current mufflers effectively suppress noise, they suffer certain drawbacks. For example, high temperature gases are typically exhausted from the APU which can cause the muffler to expand. However, many conventional mufflers do not suitably account for this expansion causing the structural integrity thereof to potentially become compromised. Additionally, some mufflers may not have a sufficient volume or optimize use of existing volumes to dampen APU noise to acceptable levels.
Therefore, there is a need for a muffler system that is capable of expanding in the aircraft in response to heat contact. There is also a need for a muffler system that optimizes available damping volume to dampen APU noise. The present invention addresses one or more of these needs.